In a gas turbine engine, ambient air is drawn into a compressor section. Alternate rows of stationary and rotating aerofoil blades are arranged around a common axis, together these accelerate and compress the incoming air. A rotating shaft drives the rotating blades. Compressed air is delivered to a combustor section where it is mixed with fuel and ignited. Ignition causes rapid expansion of the fuel/air mix which is directed in part to propel a body carrying the engine and in another part to drive rotation of a series of turbines arranged downstream of the combustor. The turbines share rotor shafts in common with the rotating blades of the compressor and work, through the shaft, to drive rotation of the compressor blades.
It is well known that the operating efficiency of a gas turbine engine is improved by increasing the operating temperature. The ability to optimise efficiency through increased temperatures is restricted by changes in behaviour of materials used in the engine components at elevated temperatures which, amongst other things, can impact upon the mechanical strength of the blades and rotor disc which carries the blades. This problem is partly addressed by shielding components from the hot combustion products with cover plates. It is also known to actively cool components by providing a flow of coolant through and/or over the turbine rotor disc and blades. It is known to take off a portion of the air output from the compressor (which is not subjected to ignition in the combustor and so is relatively cooler) and feed this to surfaces in the turbine section which are likely otherwise to suffer damage from excessive heat.
FIG. 2 shows a known arrangement for a turbine disc assembly. As can be seen from the figure, a turbine blade 9 is fed with high pressure coolant (for example compressed air which has by-passed the combustor) via a channel 2 in the disc rim. The coolant arrives at the turbine section in a chamber 8 formed by a casing under the combustor (not shown). The coolant passes through transfer holes 4 in a cover plate 5 which is arranged downstream of the chamber 8 and upstream of the main turbine disc body 10, it is then ducted radially outwards through a passage 3 which is formed between the cover plate 5 and the main turbine disc body 10. Its pressure is maintained using seals. Annular seal plate 12 suspends from an adjacent stator guide vane 13 to form, with an axial projection of the cover plate 5 a seal to prevent hot gases from the working fluid entering the region adjacent the disc body 10. The cover plate 5 is mounted at its radially inner end by means of a flange 6 which connects to a shaft on which the disc body 10 rotates and is held in position with respect to the disc body 10 by means of an annular rim 11 on the disc which defines a radially extending slot into which a radially outer edge 1 of the cover plate 5 is received. Since the coolant is directed radially outwardly in the passage 3 from the cooling holes 4 to the channel 2, a radially inner section of the disc body extending to the cooling holes 4 is shielded from oncoming work fluid and coolant.
The invention provides an alternative disc body and cover plate assembly which is expected to provide cost savings and improved engine performance/engine life extending benefits.